This invention relates to a hermetically sealed ceramic package for electronic devices. A ceramic package according to the invention is particularly suitable for packaging devices operating at high frequencies such as microwave devices, devices high in withstand voltage and devices required of very high reliability.
Alumina is prevailing as the ceramic material of conventional ceramic packages for electronic devices, and for hermetically sealing an alumina package it is usual to use a gold-tin eutectic alloy as brazing solder to braze the cap or lid of the package to the header or base. Au-Sn solder is employed because the sealing solder needs to have a higher melting point than the soft solder such as Sn-Pb solder used in the subsequent operation of connecting the leads extruding from the package to a circuit board or the like.
However, in the case of a ceramic package using a base which is copper-metallized on the top surface, the sealing of the package by Au-Sn brazing solder encounters a problem that the seal becomes insufficient by reason of alloying of Cu on the metallized surface with the Au-Sn solder. Therefore, in conventional ceramic packages formed of a low temperature fired ceramic which is lower than alumina in dielectric constant and also in thermal expansion coefficient and metallized with copper, an ordinary soft solder must be used for sealing, and the applications of such packages are limited because of the possibility of melting of the soft solder seal during the subsequent manufacturing operations on the packaged devices.